1. Field of the Invention
The present invention relates to a fuel system comprising a fuel vessel, molded parts for the fuel vessel and a tube for a fuel which are excellent in a permeation-preventing performance against an automobile fuel (gasoline barrier property), a heat resistance and an impact resistance.
2. Description of the Related Art
In recent years, practical use turned from a metal-made fuel vessel to a thermoplastic resin-made fuel vessel has positively been promoted in a fuel vessel represented by a fuel vessel for automobiles from the viewpoints of a reduction in weight, a rust preventive property, easiness in mold processing and recycling property. When a fuel vessel is loaded in automobiles, various performances such as a heat resistance, a water resistance and an impact resistance are required to the vessel, and therefore a polyethylene-single layer type tank is spread as a thermoplastic resin-made fuel tank. However, there has been involved the problem that it has a relatively high gasoline permeability, so that a gasoline component is permeated and volatilized through a fuel vessel body. Accordingly, a multilayer tank comprising polyethylene and an ethylene-vinyl alcohol copolymer (EVOH) is proposed as a vessel having an excellent gasoline barrier property (Japanese Patent Application Laid-Open No. 29904/1997), and this has made it possible to obtain a fuel vessel having a better gasoline barrier property.
However, a gasoline barrier property of the fuel vessel is not necessary satisfactory to further strengthened environmental regulation, and therefore the performance is required to be raised further more.
In general, high density polyethylene is used for producing molded parts attached to a fuel vessel (for example, a fuel tube, a degassing line in an oil filler port, a valve for removing pressure and connectors thereof to a vessel body). This allows a fuel to be permeated and volatilized through these molded parts. Accordingly, even if a fuel vessel body is provided with an excellent gasoline barrier property, there has been brought about the problem that fuel is permeated and volatilized through molded parts connected thereto, and an amount thereof can not be neglected.
It is considered to use a barrier resin in place of high density polyethylene (for example, EVOH and the like) as means for solving the above problem. When using only a barrier resin for molded parts for a fuel vessel, the problem that gasoline is permeated and volatilized can be solved, but the heat fusing property thereof to a fuel vessel body, the mechanical strength and the impact resistance become unsatisfactory. Further, molded parts of a multilayer structure comprising high density polyethylene and a barrier resin are proposed (Japanese Patent Application Laid-Open No. 52658/2002). However, all connected parts produced by heat fusion and fitting are not of a structure in which they are substantially covered with a barrier resin, and the problem that gasoline is permeated and volatilized through the above parts has not yet been solved.
Further, in recent years, fuel tubes or hoses used mainly for vehicles have had to be elevated in a fuel permeation resistance as environmental regulation is strengthened. Tubes comprising conventional rubber materials as a principal component have come to be unable to meet these requirements, and therefore in order to meet them, tubes obtained by laminating a resin layer having a low permeability against a fuel such as gasoline in the inside of tubes comprising rubber materials have been put to actual use. Known are, for example, a tube in which a tube comprising polyamide base resin is inserted into the inside of a tube comprising a rubber material to form a double layer structure, a tube in which a tube-like rubber material is vulcanizably adhered with a fluorine rubber or a fluororesin layer to form a laminated structure (Japanese Patent Application Laid-Open No. 205745/2001), a tube in which a fluorine base resin powder or a resin powder obtained by blending it with a polyamide base resin is electrostatically coated on the inner face of a tube comprising a rubber material and heated to form a resin layer (Japanese Patent Application Laid-Open No. 25578/1996) and a tube in which a solution of a fluororesin or a polyamide resin is coated on the inner face of a tube comprising a rubber material to form a resin layer (Japanese Patent Application Laid-Open No. 165360/2001).
However, in the tube having a structure in which a tube of a different layer is inserted (Japanese Patent Application Laid-Open No. 205745/2001), it is difficult to make the wall thin, and the flexibility is reduced, so that application thereof to a tube having a complicated form is difficult. In the method in which a base resin powder is electrostatically coated (Japanese Patent Application Laid-Open No. 25578/1996), it is not easy to form a homogeneous resin layer having a prescribed thickness on the inner surface of a rubber hose, and there is the problem that pinholes are produced. Further, when using fluororesins in any tubes, it is difficult to obtain the good adhesiveness with base materials for a tube such as rubber materials, and it is required to carry out separately surface treatment or use an adhesive in combination. When using a polyamide resin (Japanese Patent Application Laid-Open No. 165360/2001), the good adhesiveness with base materials for a tube such as rubber materials is obtained, but the fuel permeation resistance thereof is not satisfactory, and the performance is required to be further elevated.